(a) Field of the Invention
The present invention relates to a method for estimating channels in a wireless communication system, and an apparatus thereof.
(b) Description of the Related Art
In order to achieve coherent signal detection in a wireless communication system using a communication scheme such as orthogonal frequency division multiplexing, a receiver should know a frequency response of fading channels (called “channel frequency response” (CFR)).
Schemes for estimating a CFR include a least squares (LS) channel estimation scheme and a linear minimum mean square error (LMMSE) channel estimation scheme (LMMSE). A discrete Fourier transform (DFT)-based channel estimation scheme has been developed because of the drawbacks of these schemes.
The DFT-based channel estimation scheme obtains a channel impulse response (CIR) in a time domain by applying an inverse discrete Fourier transform (IDFT) to a CFR that is obtained based on the LS channel scheme, and performs interpolation by adding “0” to the CIR and applying a discrete Fourier transform (DFT) to the same.
In a practical communication system, direct current (DC) subcarriers are not used due to DC offset problems, and subcarriers at high frequencies are not used to avoid adjacent channel interference. These subcarriers are also called virtual subcarriers (VC).
The existence of VC means that only the LS channel estimation scheme has an effect on subcarriers in a frequency domain. Thus, the loss of channel energy in VC results in energy leakage in the time domain. Several iterative algorithms have been proposed to cope with the energy leakage problem, but all these algorithms require a block-type pilot structure.
Parts of subcarriers distributed in a downlink of a wireless communication system are not block-type pilots, but rather are comb-type pilots. If the CFR estimated by an LS algorithm using the comb-type pilots is transformed to get the CIR in the time domain, the channel energy leakage will be much more severe than that where block-type pilots are used. An iterative algorithm has been used to mitigate the negative effects caused by VC, but the number of iterations for performing processes is fairly large due to a slow convergence speed.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.